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2017
Maksymowicz, A, Chadwell CD, Ruiz J, Trehu AM, Contreras-Reyes E, Weinrebe W, Diaz-Naveas J, Gibson JC, Lonsdale P, Tryon MD.  2017.  Coseismic seafloor deformation in the trench region during the Mw8.8 Maule megathrust earthquake. Scientific Reports. 7   10.1038/srep45918   AbstractWebsite

The M-w 8.8 megathrust earthquake that occurred on 27 February 2010 offshore the Maule region of central Chile triggered a destructive tsunami. Whether the earthquake rupture extended to the shallow part of the plate boundary near the trench remains controversial. The up-dip limit of rupture during large subduction zone earthquakes has important implications for tsunami generation and for the rheological behavior of the sedimentary prism in accretionary margins. However, in general, the slip models derived from tsunami wave modeling and seismological data are poorly constrained by direct seafloor geodetic observations. We difference swath bathymetric data acquired across the trench in 2008, 2011 and 2012 and find similar to 3-5 m of uplift of the seafloor landward of the deformation front, at the eastern edge of the trench. Modeling suggests this is compatible with slip extending seaward, at least, to within similar to 6 km of the deformation front. After the M-w 9.0 Tohoku-oki earthquake, this result for the Maule earthquake represents only the second time that repeated bathymetric data has been used to detect the deformation following megathrust earthquakes, providing methodological guidelines for this relatively inexpensive way of obtaining seafloor geodetic data across subduction zone.

2010
Prawirodirdjo, L, McCaffrey R, Chadwell CD, Bock Y, Subarya C.  2010.  Geodetic observations of an earthquake cycle at the Sumatra subduction zone: Role of interseismic strain segmentation. Journal of Geophysical Research-Solid Earth. 115   10.1029/2008jb006139   AbstractWebsite

We use survey mode and continuous GPS data from 1991 to 2007 to examine fault segmentation in the earthquake cycle at the Sumatra megathrust, site of the 26 December 2004 M(w) 9.1 Sumatra-Andaman, the 28 March 2005 M(w) 8.7 Nias-Simeulue, and the 12 September 2007 M(w) 8.4 Mentawai earthquakes. These data, including new observations from 2006 and 2007, allow us to observe the final few years of one earthquake cycle and the beginning of the next. Our analysis reveals that the megathrust is segmented, a characteristic that may persist through multiple earthquake cycles. The Nias-Simeulue earthquake ruptured approximately the same region that broke in 1861, a 300 km long segment abutting the Sumatra-Andaman rupture zone. Farther southeast, the Mentawai segment of the megathrust (0.5 degrees S-5 degrees S), which produced M > 8 earthquakes in 1797 and 1833, is fully locked in the interseismic period but is flanked by two freely slipping regions, the Batu Islands in the NW and Enggano in the SE. The 12 September 2007 Mentawai earthquake sequence ruptured only the southern one third of the 1833 rupture zone. We model postseismic deformation from the Sumatra-Andaman and Nias-Simeulue earthquakes and find that afterslip was concentrated updip and downdip, respectively, from the main shocks. Comparing the velocity fields before and after 2001, we find the subduction zone underneath the Batu Islands and Enggano, which, prior to the earthquakes, was partially to fully coupled, appears now to be slipping freely. Thus, while the segmentation of the subduction zone is preserved, interseismic coupling on the subduction fault may vary with time.